Here’s the wikipedia entry on the Theremin, a musical instrument with which I’ve always been fascinated. At right, see Léon Theremin playing his creation. Theremin invented the instrument while working on a proximity detector for the Russians.
You’d know the sound of a Theremin when you hear it — think of the original “Star Trek” theme or the haunting notes at the end of to the Beach Boys’ “Good Vibrations.” The Theremin was really the first electronic synthesizer, but none of its sucessors sound quite like it — perhaps because you don’t play it with a keyboard, but by simply waving your hands or a wand around it. Seems like a tough instrument to master.